By applying advances in molecular biology and molecular genetics to population based studies of HIV-1 infection, Viral Epidemiology Branch investigators help elucidate the distribution, determinants, and natural history of this cancer-associated virus.HIV-1 RNA levels and prognosis: Using longitudinal HIV-1 RNA levels from our cohort of HIV-1- infected homosexual men, we and our collaborators demonstrated that there is a simple relationship between HIV-1 RNA levels and survival time after infection. Using specimens collected during late stage HIV-1 infection in our cohort of hemophiliacs, we demonstrated that HIV-1 RNA levels predict disease progression independently of CD4+ lymphoctye counts. These data, which suggest that the HIV-1 RNA level reflects the current level of immunosuppression, may be useful for determining clinical prognosis and treatment. Chemokine receptors and HIV: Our intensive evaluation of a group of HIV- 1-uninfected subjects who were homozygous for the CCR5-delta32 allele demonstrated that CCR5-delta32/delta32 homozygotes are generally similar to wild-type persons. Confirmatory investigations are required to determine if hypertension, increased lymphocyte counts, and higher hepatic enzyme levels in the presence of HCV infection represent true phenotypic expressions of this genotype. We collaborated in the discovery that a mutation in the CCR5 promoter region gene was associated with faster progression to AIDS. We expanded the international meta-analysis of the effect of host genetics on HIV disease progression. The meta-analysis seeks to increase statistical precision over that available from any single study. - Human Subjects & Human Subjects: Minor under 18 Years Old & Human Subjects: Interview, Questionaires, or Surveys Only & Human Tissues, Fluids, Cells, etc.